The carbon cycle circulates the element carbon through all of Earth's spheres. The carbon cycle circulates carbon through all of earth's spheres - from the atmosphere to the biosphere to the geosphere & hydrosphere, and back to the atmosphere. Carbon is an essential ingredient to life and helps protect life by giving us the greenhouse effect, which keeps our planet's surface warm and habitable. However, humans are altering the carbon cycle, mainly by contributing carbon dioxide to the atmosphere at a faster rate than is being removed by other processes.

Organisms pass carbon dioxide back and forth through the processes of photosynthesis and respiration. Humans are greatly influencing the carbon cycle. Humans are altering the carbon cycle by releasing once-stored carbon dioxide back to the atmosphere by burning fossil fuels and deforestation

Plants, seawater, the seafloor, and Earth's crust are common "stores" of carbon (places where carbon is removed from the carbon cycle for an extended period of time). Scientists are exploring each of these stores to find a way of sequestering carbon dioxide, preventing it from entering the atmosphere, and therefore lessening the impacts of global warming. There are several methods of carbon sequestration being considered, and each has its benefits and drawbacks.